The CAN bus system has become widely used for communication between sensors and control units. For example, the CAN bus system is utilized in automobiles. In the CAN bus system, messages are transmitted with the aid of the CAN protocol, as is described in ISO11898. Automotive bus systems, in particular, are being continuously developed toward greater bandwidths, shorter latency times, and stricter real-time capability. In addition, technologies were recently proposed for this purpose, such as, for example, CAN FD, in which messages are transmitted according to the specification “CAN with Flexible Data-Rate, Specification Version 1.0” or corresponding to ISO11898-1 which is currently being revised (presently available as ISO11898-1 CD), etc. In such technologies, the maximum possible data rate is increased to a value greater than 1 MBit/s by using a higher clock pulse in the area of the data fields. Such messages are also referred to in the following as CAN FD frames or CAN FD messages.
The expansion of the CAN standard was not only supplemented primarily with functions, such as, e.g., TTCAN, the CAN standard but was also recently expanded further with CAN FD, particularly with respect to the possible (higher) data rate and the usable data packet size, the inherent CAN properties being retained, particularly in the form of the arbitration.
Problems exist at this time with regard to a calculation of the checksum of a CAN FD frame when the identifier of the CAN FD frame begins with four dominant bits. These four dominant bits, together with one dominant starting bit of the CAN FD frame, which is also referred to as the start-of-frame bit, form a so-called stuff condition, according to which a recessive stuff bit is inserted between the fourth and fifth bits of the identifier. In this case, if the dominant starting bit of the CAN FD frame is overwritten locally with a recessive bit in a recipient of the CAN FD frame, the recipient of the CAN FD frame interprets the first dominant bit of the identifier as the starting bit of the frame. Since there is no stuff condition in the recipient due to the received recessive stuff bit, the recipient will accept the recessive stuff bit as the fourth bit of the identifier. The next bit is accepted as the fifth bit of the identifier and the recipient will be back in phase with the sender. In this case, however, the changed fourth bit of the identifier is not recognized in the checksum at the end of the CAN FD frame. For example, an identifier 0x001 transmitted by the sender is received by the recipient as 0x081. This applies both for the 11-bit identifier and for the 29-bit identifier in the case of CAN FD.